Provided are compositions and methods for water-based drilling fluids. More particularly, compositions and methods are provided for water-based drilling fluids comprising a betaine shale stabilizer.
During the drilling of a wellbore into a subterranean formation, a drilling fluid, also referred to as a drilling mud, may be continuously circulated from the surface down to the bottom of the wellbore being drilled and back to the surface again. Among other functions, the drilling fluid may serve to transport wellbore cuttings up to the surface, cool the drill bit, and provide hydrostatic pressure on the walls of the drilled wellbore. Drilling fluids may be used in shale formations comprising water-swellable shales, which may also be referred to as water-swellable clays. As the water-swellable shales are exposed to water, they may swell and consequently increase wellbore pressure. On the extreme end, an increase in wellbore pressure may create a dangerous wellbore condition which could result in an explosion. Lesser increases in wellbore pressure may cause formation damage or may increase the drilling fluid viscosity to a point where further drilling becomes difficult.
To stabilize the water-swellable shales a variety of shale stabilizers may be added to the drilling fluid. Examples of shale stabilizers include short chain amines, polymeric amines (e.g., polyacrylamide), and quaternary ammonium ions. However, these shale stabilizers may be toxic at the concentrations necessary for shale stabilization, thus posing a risk to personnel and the environment. Further, the shale stabilizers may not be biodegradable and/or biocompatible. Thus, the shale stabilizers may pollute the environment, formation, water table, etc., which may lead to increased cleanup costs. Further, many of the aforementioned shale stabilizers are expensive and their cost may limit the types of wells that may be drilled and may also reduce overall profitability of the operation.